Canoes, pirogues, skiffs, dinghies, and similar shallow-draft boats are often used by fishermen or recreational boaters to paddle easily through reaches of shallow water that may be too narrow for rowing or that may be clogged to varying degrees by vegetation and debris. To reduce effort and speed their rate of travel, many boaters attach outboard electric trolling motors to their craft. Electric trolling motors are lightweight, efficient, and virtually silent, and derive their power from batteries or other sources of electric power carried in the boat.
Efficiency of the motor's operation is a critical factor in the utility of such electric motors, since batteries are heavy, and since other sources of electricity such as solar panels are dependent on the intensity of the light they receive. The more efficient the motor, the greater the time the boat may be operated away from its sources of charging. The greater the time between charges, the greater is the range of the boat's possible travel.
Most electric trolling motors are contained in a waterproof cylindrical housing, and drive a propeller at the aft end of the housing. The propeller is used to push the motor and thus the boat through the water. For the electric trolling motor to operate most efficiently, it must be immersed in the water so that its propeller blades are also fully immersed in the water where the flow of water is least disrupted by the boat hull or other parts of the boat that lie directly ahead of the motor and propeller. Although this problem is of less concern with canoe hulls, it is more important in other less-streamlined hull designs. Mounting the motor in the undisrupted water flow confronts a second problem: the presence of debris or vegetation in the path of the boat. Often the motor or propeller can become fouled in plants or lines, or can be damaged by striking hard objects that pass beneath the boat's hull as it moves.
For those boats having a flat stern panel, such as square-stern rowboats or skiffs, the outboard trolling motor is customarily clamped or otherwise mounted to the flat stern piece at the longitudinal centerline or keel line of the boat. For those boats having a pointed stern, such as canoes or pirogues, the outboard trolling motor is customarily clamped or mounted to an external part of a stern crosspiece on one side or the other of the boat. Such mountings place the motor on the side of the pointed stern.
The mounting of a motor on one side of the boat stern introduces a problem with steering. Since the motor is on one side, its thrust along the longitudinal axis of the boat will tend to turn the boat toward the other side. Consequently the tendency to turn the boat must be countered by adjusting the motor orientation, the boat's rudder, or any other steering device used. Such adjustments must vary according to the motor speed and thrust, the wind, and other factors affecting the course of the boat.
From the above observations, there is an evident need for a propulsion system that retains the efficiency, quiet, speed, and other desirable characteristics of the conventional art, while protecting the motor, propeller and mountings from submerged obstacles and debris, and eliminating problems associated with mounting the motor on the side of the boat.